I was thinking of buying the A. Ness O.P. gauge that mounts on rocker of the Twin Cam Dyna engine. It says it does not fit billet rockers. I bought my bike used. (2007 Street Bob) How can one tell if they are billet ? Mine has some weathering on them and I recently polished them when I took the tank off. But I have no idea if they are billet or not ?